1. Field of the Invention:
This invention relates to a reflection mirror for optical instruments and particularly single lens reflex cameras.
2. Description of the Prior Art:
The conventional 45.degree. mirror assembly has, as illustrated in FIG. 1, a polished-deposited glass 1 supported on a punched-and-formed metal plate 2 held in fixedly secured relation by an adhesive and further by retainer leaf springs 3 caulked to this plate 2. Mirror pivot shafts 4 and a mirror flip-up pin 5 are mounted on a pair of supplementary members 6 which are in turn caulked to the plate 2. Thus, as regards the essential parts alone, the mirror assembly necessitates 14 components and involves a very complicated form. Then, the mirror in the rigidly secured state must be so flat as to be optically acceptable. To achieve this, not only the glass 1, but also the metal plate 2 is required to be machined to a high-precision flatness, thereby giving rise to the disadvantage that the production cost is increased. When the glass is adhered, the adhesive when solidified shrinks causing deterioration of the flatness. Also as the ambient temperature changes, the difference between the thermal expansion coefficients of the glass and the metal contributes to a loss in the flatness, and as a result, the glass is often caused to peel off from the metal plate. Under very severe working conditions, a crack or similar phenomenon will appear in the glass.